Diagnosis
The control box lost its memory. This happens after a power interruption or sometimes if you try to set a preset while the desk is still moving.
How to Fix It
You need to reprogram the presets from scratch. First, move the desk to your desired standing height using the up/down buttons. Press and hold the "M" button until it beeps, then immediately press and hold the "1" button until it beeps twice. That saves the height to preset 1. Repeat for preset 2 with your sitting height. It has to be done in this specific hold-then-hold sequence.
If That Didn't Work
If the keypad just beeps angrily and doesn't save, the desk might need a full recalibration. Unplug the desk. Hold down the "Down" arrow button on the keypad and, while holding it, plug the power back in. Keep holding for about 10 seconds until the desk jogs down and then back up a bit. This resets the height memory to factory, then you can try setting presets again.
Heads Up
The preset buttons only save a height position. They don't save other settings like anti-collision sensitivity. If the desk stops and reverses before hitting your saved preset, that's the anti-collision kicking in, not a bad memory.